The invention relates generally to sheet handling devices and, more particularly, to detecting and compensating for wear in the sheet handling components of those devices.
Sheet handling devices such as printers, copiers, and sorters/stackers generally use one or more friction transport rollers to transport sheets through the device. These rollers are driven at a constant angular velocity using a stepper motor or, in some instances, a DC motor. The linear transport speed of sheets passing through the device then becomes a function of the diameter of the rollers. Unfortunately, extended use of the device causes the rollers to wear and decrease in size. Once the diameter of a transport roller becomes too small, the device ceases to function properly.
As a function of the number of sheets passing through a device, the diameter d of a transport roller can be represented by the following equation.
d(Ksh)=dn*exe2x88x92Kw*Ksh
The constant dn represents the nominal or original diameter of the transport roller. The factor Kw is a constant that depends upon a number of factors such as the material of the transport roller, the friction between the roller and the sheets, and the speed at which the roller is driven. The symbol Ksh represents the number of sheets that have passed through the device. The linear transport speed Ts at which the transport roller can move a sheet can then be represented by the following equation.
Ts=xcfx80*d(Ksh)*Av
Av represents the angular velocity at which the transport roller is driven. Combining the above two equations reveals the following.
Ts=xcfx80*dn*exe2x88x92Ks*Ksh*Av
Consequently, as long as the angular velocity Av remains constant, the transport speed Ts will decrease through use of the device.
Market demands require ever increasing life spans for electronic devices. Consequently, to increase the life span of sheet handling devices a method and system embodying that system are needed to compensate for transport roller wear increasing the life of sheet handling devices.
Accordingly, the present invention is directed to a method and system to regulate the sheet transport speed in a sheet handling device. Sheets are transported at a transport speed governed by an assigned signal. The actual transport speed of the sheets is determined and the assigned signal is adjusted to make the actual transport speed match a desired transport speed.